Systems and methods to provide enhanced diode bypass paths

ABSTRACT

Systems and methods are herein disclosed for efficiently allowing current to bypass a group of solar cells having one or more malfunctioning or shaded solar cells without overwhelming a bypass diode. This can be done using a switch (e.g., a MOSFET) connected in parallel with the bypass diode. By turning the switch on and off, a majority of the bypass current can be routed through the switch, which is configured to handle larger currents than the bypass diode is designed for, leaving only a minority of the current to pass through the bypass diode.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. patentapplication Ser. No. 13/235,064, filed Sep. 16, 2011 and entitled“SYSTEMS AND METHODS TO PROVIDE ENHANCED DIODE BYPASS PATHS”, now U.S.Pat. No. 9,425,783, issued on Aug. 23, 2016, which claims the benefit ofProv. U.S. Pat. App. Ser. No. 61/440,342, filed Feb. 7, 2011 andentitled “Systems and Methods to Provide Enhanced Diode Bypass Paths,”the disclosures of which are incorporated herein by reference.

The present application relates to U.S. patent application Ser. No.12/724,371, filed Mar. 15, 2010 and entitled “Systems and Methods toProvide Enhanced Diode Bypass Paths,” the disclosure of which isincorporated herein by reference.

FIELD OF THE TECHNOLOGY

At least some embodiments of the disclosure relate to limiting currentin bypass diodes of a solar energy generating system.

BACKGROUND

Solar cells can be connected in series to form strings. When one or moresolar cells in the string malfunction or are shaded from sunlight, themalfunctioning or shaded solar cells become highly resistive. As aresult, other solar cells in the string may not generate enough voltageto overcome the resistive cells and thus current will cease to passthrough the string. Bypass diodes can be connected in parallel withgroups of solar cells (one or more solar cells connected in series) toallow current to bypass groups of solar cells having one or more highlyresistive solar cell. In this way, current can continue to run throughthe string even when one or more solar cells malfunction or are shaded.However, large and efficient solar modules generate such large currentsthat when these large currents pass through the bypass diodes there areunwanted power losses and heat, and even bypass diode damage. Even lowloss diodes (e.g., Schottky diodes) may not be able to overcome thelosses, heat, and potential damage.

U.S. Pat. App. Pub. No. 2011/0068633, published on Mar. 24, 2011,discloses a protective circuit for a solar module. The protectivecircuit includes a trigger circuit and a switching arrangement, which inthe case of shading of the solar cells is activated to provide a currentbypass.

SUMMARY OF THE DESCRIPTION

Systems and methods to allow high currents to efficiently pass bypassdiodes in solar modules are described herein. Some embodiments aresummarized in this section.

In one embodiment, systems and methods are herein disclosed forefficiently allowing current, or a bypass current, to bypass a group ofsolar cells having one or more malfunctioning or shaded solar cellswithout overwhelming a bypass diode. This can be done using a switch(e.g., a metal-oxide semiconductor field-effect transistor) connected inparallel with the bypass diode. By turning the switch on, a majority ofthe bypass current can be routed through the switch, which is configuredto handle larger currents than the bypass diode is designed for, and aminority of the current can be routed through the bypass diode.

In one embodiment, a small amount of power from the bypass current isused to power the switch and/or a controller configured to turn theswitch on and off. A capacitor can be connected to a control of theswitch (e.g., the gate of a metal-oxide semiconductor field-effecttransistor) through a latch circuit. When the latch is closed or off,the capacitor cannot discharge and close, or turn on, the switch. Whenthe latch is open or on, the capacitor can discharge and close, or turnon, the switch. The latch turns on when the capacitor voltage has beencharged to above a first voltage threshold. With the switch turned on, amajority of the bypass current passes through the switch rather thanthrough the bypass diode.

In one embodiment, a current and voltage spike generated when the switchcloses can be used to power the switches. As the capacitor discharges,the voltage across the capacitor decreases until the voltage falls belowa second voltage threshold (the second voltage threshold is lower thanthe first voltage threshold). When this happens, the latch circuit turnsoff and prevents the capacitor from discharging. Without the capacitorvoltage reaching the switch, the switch turns off. This causes a currentand voltage spike through the bypass diode. A portion of this currentand voltage spike can be used to recharge the capacitor until thevoltage across the capacitor again rises above the first voltagethreshold. The latch circuit then opens again, the switch turns on, andthe cycle begins again.

In one embodiment, a system includes a group of series-connected solarcells, a bypass diode, and a bypass switch. The bypass diode can beconnected in parallel to the group of series-connected solar cells. Thebypass switch can be connected in parallel to the group of solar cellsand the bypass diode. The bypass switch can be configured to allow abypass current to bypass the group of solar cells and the bypass diode.

In one embodiment, a system includes one or more bypass diodes and oneor more bypass transistors. The one or more bypass diodes can beconnected in series with one another and connected in parallel with agroup of series-connected solar cells. The one or more bypasstransistors can be connected in parallel with the one or more bypassdiodes. The one or more bypass transistors can be configured to turn onfor a predetermined time period, in response to a bypass current passingthrough the one or more bypass diodes and to reroute the bypass currentfrom the one or more bypass diodes to the one or more bypasstransistors.

In one embodiment, a method includes charging a capacitor of acontroller in response to a bypass current passing through a bypassdiode. The method also includes opening a latch circuit of thecontroller when a voltage across a capacitor of the controller exceeds afirst voltage threshold. The method also includes applying a portion ofthe voltage to gates of a pair of bi-directional MOSFETs to turn onbi-directional MOSFETs via the opening of the latch circuit. Thebi-directional MOSFETs are connected to the diode to reduce the currentpassing through the diode when the bi-directional MOSFETs are turned on.The method also includes closing the latch circuit when the voltageacross the capacitor falls below a second voltage threshold to turn offthe bi-directional MOSFETs. The second voltage threshold can be lowerthan the first voltage threshold.

In one embodiment, a system includes a solar panel having a set of solarcells and a bypass switch circuit connected to the set of solar cells.The bypass switch circuit is configured to allow a bypass current tobypass the set of solar cells that are not producing sufficient power.The bypass switch circuit includes a bypass transistor connected inparallel with an output of the set of solar cells, which transistor whenactivated, provides a path for the bypass current. In one embodiment,the bypass transistor is a MOSFET having a parasitic diode; the bypassswitch circuit further includes a first diode connected to receive theoutput of the set of solar cells and configured to be conductive whenthe parasitic diode of the bypass transistor is conductive; and thebypass switch circuit further includes a control circuit coupled withthe bypass transistor and the first diode to activate the bypasstransistor in response to the parasitic diode of the bypass transistorbecoming conductive. In one embodiment, the control circuit includes anenergy storage device connected to the first diode and, when theparasitic diode is conductive, charged to provide a voltage to a voltageconverter. The voltage converter, which can be a single cell converter,is connected to the energy storage device and generates a convertedvoltage to power a controller. The controller uses the converted voltageto control the bypass transistor. In one embodiment, once the bypasstransistor is activated, the controller is configured to deactivate thebypass transistor after a predetermined time period has elapsed. Thispredetermined time period is based at least in part on a voltage on theenergy storage device. The energy storage device can be a capacitor,which is connected to be charged using a voltage drop difference betweenthe parasitic diode and the first diode. In one embodiment, when thecurrent bypasses the set of solar cells, the ratio of the time period inwhich the parasitic diode of the bypass transistor is in a conductivestate, to the subsequent time period in which the controller keeps thebypass transistor in an activated state, is less than 1:100. In oneembodiment, the solar panel further includes a low dropout regulatorconnected to receive the output from the set of solar cells, andconfigured to supply power to the controller when the parasitic diode isnot conductive (e.g., when the solar cells are functioning properly toproduce sufficient power in a string of series-connected solar panels).

In one embodiment, a bypass switch circuit includes: a bypass transistorhaving a parasitic diode, the bypass transistor to be connected inparallel with an output of a group of solar cells; a first diode; afirst capacitor connected in series with the first diode, where a pathformed by the first diode and the first capacitor is connected inparallel with the bypass transistor; a single cell converter connectedto the first capacitor to receive an input, the single cell converter togenerate an output; a second diode connected to receive the output ofthe single cell converter; a second capacitor connected in series withthe second diode; and a controller connected to the second capacitor andconfigured to turn on the bypass transistor in response to the parasiticdiode being conductive. In one embodiment, the bypass switch circuitfurther includes a voltage regulator configured to use the output of thegroup of solar cells to power the controller when the parasitic diode isnot conductive, and the voltage regulator is a low dropout regulator.The time periods to charge and discharge the first and second capacitorsdetermine the duty cycle of the bypass transistor. In one embodiment,after a first time period in which the parasitic diode of the bypasstransistor is conductive, the controller activates the bypass transistorfor a second time period, and a ratio between the first time period andthe second time period is less than 1:100. One embodiment furtherincludes a timer coupled with the controller to control a length of atime period during which the controller keeps the bypass transistoractivated. The first diode is configured to be conductive when theparasitic diode of the bypass transistor is conductive; and when theparasitic diode of the bypass transistor is reverse biased, the firstdiode is reverse biased.

In one embodiment, a method for controlling electric currents in aphotovoltaic system includes: charging a first capacitor, in response tobypass current passing through a parasitic diode of a transistorconnected in parallel to an output of a group of solar cells, using afirst diode powered by a voltage drop across the parasitic diode;converting a first voltage across the first capacitor to generate asecond voltage; charging a second capacitor using the second voltage;powering a controller using the second capacitor; and activating thetransistor using the controller to reduce a voltage drop across thetransistor, after the first capacitor and the second capacitor arecharged to a predetermined level. In one embodiment, the first diode isnot conductive when the transistor is activated, and the method alsoincludes discharging the first capacitor and the second capacitor afterthe voltage drop across the transistor is reduced, and deactivating thetransistor after the first capacitor and the second capacitor aredischarged to a predetermined level.

Other features will be apparent from the accompanying drawings and fromthe detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments are illustrated by way of example and not limitation inthe figures of the accompanying drawings in which like referencesindicate similar elements.

FIG. 1 illustrates an embodiment of switches connected in parallel tobypass diodes.

FIG. 2a illustrates an embodiment of a pair of bi-directional bypassswitches obtaining power from current passing through a bypass diode.

FIG. 2b illustrates embodiments of a current transformer, a powersupply, and a latch circuit.

FIG. 3 illustrates an embodiment of a bypass switch circuit having apair of bi-directional bypass switches obtaining power from a voltagedrop across a pair of bypass diodes.

FIG. 4 illustrates an embodiment of a method for bypassing bypass diodesin a solar energy generating system.

FIG. 5 illustrates a timing chart for the voltage through any one of thebypass diodes illustrated in FIG. 1.

FIG. 6 illustrates an exemplary enhanced bypass switch circuit, whichcan be used to implement the enhanced diode bypass paths for examplesuch as illustrated in FIGS. 1 and 3. For example, the circuit of FIG. 6can be used to implement the system 300 in FIG. 3.

FIG. 7 illustrates an embodiment of a method for controlling electriccurrents in a photovoltaic system.

DETAILED DESCRIPTION

The following description and drawings are illustrative and are not tobe construed as limiting. Numerous specific details are described toprovide a thorough understanding. However, in certain instances, wellknown or conventional details are not described in order to avoidobscuring the description. References to one or an embodiment in thepresent disclosure are not necessarily references to the sameembodiment; and, such references mean at least one. Similarly, variousrequirements are described which may be requirements for one embodimentbut not other embodiments. Further, unless excluded by explicitdescription and/or apparent incompatibility, any combination of variousfeatures described in this description is also included here.

FIG. 1 illustrates an embodiment of switches connected in parallel tobypass diodes. The system 100 illustrated in FIG. 1 includes a solarmodule 102 having four groups of solar cells 112, 114, 116, 118. Eachgroup of solar cells 112, 114, 116, 118 is connected in series with anadjacent group of solar cells 112, 114, 116, 118. The solar module 102is part of a string of solar modules, and is series (or parallel)connected to other strings via the string terminals 104, 106. Each groupof solar cells 112, 114, 116, 118 is connected in parallel with a bypassdiode 122, 124, 126, 128. If a solar cell within any one of the groupsof solar cells 112, 114, 116, 118 becomes too resistive, either due tomalfunction, shading, or other causes, current passes through the bypassdiode 122, 124, 126, 128 rather than the high resistance group of solarcells 112, 114, 116, 118. However, the bypass diodes 122, 124, 126, 128are resistive enough that high currents passing through them can causeunwanted heat (lost power) and damage to the bypass diodes 122, 124,126, 128. To avoid these losses and damage, bypass switches 142, 144,146, 148 (e.g., metal-oxide semiconductor field-effect transistors) caneach be connected in parallel with one of the bypass diodes 122, 124,126, 128 and to one of the groups of solar cells 112, 114, 116, 118. Forinstance, the first bypass switch 142 is connected in parallel with thefirst bypass switch 122 and the first group of solar cells 112.

For the sake of clarity, the next few paragraphs will describe only thefirst bypass switch 142, the first bypass diode 122, and the first groupof solar cells 112. The bypass switch 142 can be normally in an open (oroff) state when the group of solar cells 112 operates normally. When thegroup of solar cells 112 becomes too resistive, and current passesthrough the bypass diode 122, the bypass switch 142 can be closed (orturned on) so that a majority of the current passes through the bypassswitch 142 rather than through the bypass diode 122. The bypass switch142 can be configured to allow the current through the bypass diode 122,also known as a bypass current, to pass through the bypass switch 142rather than the bypass diode 122 or the group of solar cells 112. Bypasscurrent is current that passes through a bypass diode 122, 124, 126, 128or a bypass switch 142, 144, 146, 148 rather than a group of solar cells112, 114, 116, 118. In an embodiment, the bypass switch 142 isconfigured to turn on and off periodically. Thus, when the bypass switch142 is off (open), bypass current primarily passes through the bypassdiode 122. When the bypass switch 142 is on (closed), bypass currentprimarily passes through the bypass switch 142. However, the duty cycleof the bypass switch 142 is such that the bypass current passes throughthe bypass switch 142 more often than the bypass current passes throughthe bypass diode 122.

The bypass switches 142, 144, 146, 148 can be any electrical devicehaving low resistance or impedance when in a closed state (the on state)and high impedance in an open state (the closed state). For instance, inan embodiment, the bypass switches 142, 144, 146, 148 are transistors.In an embodiment, the bypass switches 142, 144, 146, 148 are metal-oxidesemiconductor field-effect transistors (MOSFETs), although other typesof electrical switches can also be implemented. Because of the lowimpedance of the bypass switches 142, 144, 146, 148, there is littlevoltage drop or heat generated when the bypass current passes throughthe bypass switches 142, 144, 146, 148. The bypass switches 142, 144,146, 148 ideally pass most of the bypass current so that the bypassdiodes do not generate heat and waste power. This also prevents damageto the bypass diodes 122, 124, 126, 128. While the bypass switches 142,144, 146, 148 are illustrated as enhancement mode n-type MOSFETs, itshould be understood that any type of switch having a low-loss (or lowimpedance) on state can be used.

Each bypass diode 122, 124, 126, 128 can have a positive and a negativeterminal. When forward biased, there is a voltage drop from the negativeterminal to the positive terminal. In other words, current passesthrough the bypass diodes 122, 124, 126, 128 from each bypass diode'snegative terminal to each bypass diode's positive terminal.

In an embodiment, the bypass diodes 122, 124, 126, 128 and the bypassswitches 142, 144, 146, 148 are in a junction box 110. A junction box isa container in which electrical connections are made that protectsliving entities from contact with the connections. The junction box caninclude a bypass circuit 140. The bypass circuit includes the bypassswitches 142, 144, 146, 148 and a controller 150.

The controller 150 can be configured to turn the bypass switches 142,144, 146, 148 on and off. In an embodiment, the controller 150periodically turns the bypass switches 142, 144, 146 on and off. In anembodiment, the controller 150 can control duty cycles of the bypassswitches 142, 144, 146, 148. The controller 150 can send electricalsignals or pulses to the bypass switches 142, 144, 146, 148 to controlwhen the bypass switches 142, 144, 146, 148 open and close. If thebypass switches 142, 144, 146, 148 are field-effect transistors, thenthe controller 150 can control the bypass switches 142, 144, 146, 148through gates of the field-effect transistors. If the bypass switches142, 144, 146, 148 are bipolar junction transistors, then the controller150 can control the bypass switches 142, 144, 146, 148 through the basesof the bipolar junction transistors.

In an embodiment, the control 150 can hold one or more of the bypassswitches 142, 144, 146, 148 on (closed) for a period of time, then turnthe one or more of the bypass switches 142, 144, 146, 148 off (open),then turn the one or more bypass switches 142, 144, 146, 148 back onwhen the bypass current passes through one of the bypass diodes 122,124, 126, 128. For instance, if a leaf falls onto the solar module 102and blocks light from reaching the first group of solar cells 112,bypass current will pass through the first bypass diode 122. Thecontroller 150 may sense the bypass current in the first bypass diode122 and turn the first bypass switch 142 on. The leaf may then blow awayallowing current to pass through the first group of solar cells 112rather than through the first bypass diode 122 or the first bypassswitch 142. The controller 150 may hold the first bypass switch 142 onfor a period of time even though bypass current is no longer passingthrough the first bypass diode 122 or the first bypass switch 142. Thecontroller 150 may then turn the first bypass switch 142 off after aperiod of time. Later, the first group of solar cells 112 may againbecome shadowed or malfunction and cause bypass current to again passthrough the first bypass diode 122. The controller 150, sensing thebypass current in the first bypass diode 122, can turn the first bypassswitch 142 back on allowing the bypass current to pass through the firstbypass switch 142 rather than the first bypass diode 122.

The controller 150 can monitor or measure current and voltage drop. Thecontroller 150 can monitor voltage across each bypass diode 122, 124,126, 128. The controller 150 can monitor temperature in the junction box110. The controller 150 can turn one or more of the bypass switches 142,144, 146, 148 on when the temperature in the junction box 110 exceeds apredefined temperature. The controller 150 can turn one of the bypassswitches 142, 144, 146, 148 on when a voltage across one of the bypassdiodes 122, 124, 126, 128 exceeds a predefined voltage. For instance,when the voltage across the first bypass diode 122 exceeds a predefinedvoltage, the controller 150 can turn the first bypass switch 142 on,allowing current to pass through the first bypass switch 142 and causingthe voltage across the first bypass diode 122 to drop below thepredefined voltage. In an embodiment, the controller 150 can be poweredvia controller power connections 160, 162 enabling current to be drawnfrom the bypass current and/or the solar module 102.

One skilled in the art will recognize that the illustrated embodiment isillustrative only. The number of elements and/or components used ismeant only to illustrate and is not to be taken as limiting. Forinstance, instead of four groups of solar cells 112, 114, 116, 118, eachwith a bypass diode 122, 124, 126, 128 and a bypass switch 142, 144,146, 148 connected in parallel, there could be two, three, five or anynumber of groups of solar cells 112, 114, 116, 118 along with theirrespective bypass diodes 122, 124, 126, 128 and bypass switches 142,144, 146, 148. There can also be more than one bypass diode 122, 124,126, 128 for each group of solar cells 112, 114, 116, 118. There can bemore than one bypass switch 142, 144, 146, 148 for each group of solarcells 112, 114, 116, 118. There can also be systems where one bypassswitch 142, 144, 146, 148 is connected in parallel with more than onegroup of solar cells 112, 114, 116, 118 and more than one bypass diode122, 124, 126, 128.

FIG. 5 illustrates a timing chart for the voltage through any one of thebypass diodes illustrated in FIG. 1. The switches are turned on for twosecond intervals and turned off for twenty millisecond intervals. Inother words, current passes through the bypass switches for a time thatis one hundred times as great as the time that current passes throughthe bypass diodes. When the bypass switches are on, the voltage acrossthe bypass diodes drops by less than one hundred millivolts (assuming aten amp current). This low voltage drop keeps heat dissipation in thejunction box low.

The bypass switches 142, 144, 146, 148 may need power in order tooperate. FIGS. 2a, 2b , and 3 and the following discussion describeembodiments for efficiently obtaining this power. The overall operationof the embodiments in FIGS. 2a, 2b and 3 are the same as the embodimentin FIG. 1: bypass switches are turned on and off in order to allow aportion of the bypass current to bypass one or more groups of solarcells and to bypass one or more bypass diodes and instead pass throughbypass switches.

FIG. 2a illustrates an embodiment of a pair of bi-directional bypassswitches obtaining power from current passing through a bypass diode.Like the system 100 illustrated in FIG. 1, system 200 includes a solarmodule 202. The solar module 202 includes two or more groups of solarcells connected in series (not illustrated). Each group of solar cellshas a bypass diode connected to it in parallel. Only one bypass diode214 is illustrated in FIG. 2a in order to simplify the drawing andenable the drawing to focus on the details of powering and controllingthe switchable connection, or bypass switch. The six zigzag symbols atthe ends of connections or wires indicate connections to wires,circuits, or devices that are not illustrated. These connections are notopen or disconnected.

While FIG. 1 showed an embodiment where each bypass diode was connectedin parallel with a single bypass switch, FIG. 2a illustrates anembodiment where the bypass diode 214 is connected in parallel with twoswitchable connections 262, 266. The two illustrated switchableconnections 262, 266 are enhancement mode n-type MOSFETs and are thusturned on when a sufficiently high voltage is applied to the gates ofthe pair of MOSFETs 262, 266. The two switchable connections 262, 266are bi-directional in order to prevent bypass current passing through anintrinsic diode of the MOSFETs 262, 266 before the MOSFETs 262, 266 areturned on. While the two switchable connections 262, 266 are illustratedas enhancement mode n-type MOSFETs, it should be understood that othertypes of transistors and other switchable connections can also be used.For the purposes of this non-limiting embodiment, the switchableconnections 262, 266 will be referred to as MOSFETs. In an embodiment, asingle MOSFET can be implemented.

In order to power the MOSFETs 262, 266 the system 200 can include acurrent transformer 220, a power supply 230, and a latch circuit 240.The current transformer 220 generates a power supply input voltage 229when a first bypass current 250 through the bypass diode 214 increasesor spikes (e.g., when the MOSFETs 262, 266 turn off). This increase inbypass current 250 through the bypass diode 214 causes the power supplyinput voltage 229 to increase. This increase charges the power supply230. As the power supply 230 is charged, the latch input voltage 239increases. When the latch input voltage 239 rises above a first voltagethreshold, the latch circuit 240 is configured to discharge the powersupply 230 into a first gate of the first MOSFET 262 and a second gateof the second MOSFET 266. In other words the latch circuit 240 is in theon state and provides a control voltage to the gates of the first andsecond MOSFETs 262, 266. This turns the first and second MOSFETs 262,266 on and allows a second bypass current 252 to pass through theMOSFETs 262, 266. At this point, the second bypass current 252 isgreater than the first bypass current 250. While the first and secondMOSFETs 262, 266 are on and passing the second bypass current 252, thefirst bypass current 250 through the bypass diode 214 drops to near zeroamperes since the bypass diode 214 typically has a higher voltage dropthan the combined voltage drop across the first and second MOSFETs 262,266.

The power supply 230 discharges into the gate terminals of the first andsecond MOSFETs 262, 266, and the power supply 230 decreases voltage(meaning that the latch input voltage 239 decreases). Once the first andsecond MOSFETs 262, 266 are on, there is little change in the currentthrough the bypass diode 214, and thus the power supply 230 is notrecharged. When the latch input voltage 239 falls below a second voltagethreshold, that is lower than the first voltage threshold, the latchcircuit 240 is in the off state which causes the first and secondMOSFETs 262, 266 to be in the off state. As a result, the second bypasscurrent 252 through the MOSFETs 262, 266 goes to near zero amperes.Instead, bypass current primarily passes through the bypass diode 214.Furthermore, when the first and second MOSFETs 262, 266 turn off, thefirst bypass current 250 sees a rapid current increase or current spike(voltage across the bypass diode 214 also rapidly increases or spikes).A portion of this current spike is passed through the currenttransformer 220 to the power supply 230 which recharges the power supply230. The portion of the current spike charges the power supply 230 untilthe latch input voltage 239 again exceeds the first voltage threshold.At that point, the first and second MOSFETs 262, 266 are turned back on.

This process periodically turns the first and second MOSFETs 262, 266 onand off with the first and second MOSFETs 262, 266 being on a majorityof the time. Only a fraction of time elapses while the MOSFETs 262, 266are off. Thus, bypass current only passes through the bypass diode 214for a small fraction of time. Losses from high current passing throughthe bypass diode 214 and potential damage to the bypass diode 214 canthus be avoided.

The current transformer 220 charges the power supply 230 whenever thefirst bypass current 250 through the bypass diode 214 increases (adecrease in the first bypass current 250 would cause the currenttransformer 220 to discharge the power supply 230 except that the powersupply is configured to only allow current to pass in a direction thatcharges the power supply 230, for instance via use of a diode). Thelatch circuit 240 prevents the power supply 230 from discharging untilthe power supply 230 reaches a certain voltage. This occurs when thelatch input voltage 239 is greater than or exceeds the first voltagethreshold. When this happens, the latch circuit 240 allows the powersupply 230 to discharge into the gates of the first and second MOSFETs262, 266. This turns the first and second MOSFETs 262, 266 on. Thebypass current begins passing through the first and second MOSFETs 262,266 instead of through the bypass diode 214. The power supply 230discharges its voltage into the gates of the first and second MOSFETs262, 266 until the latch input voltage 239 drops below the secondvoltage threshold. When this happens, the latch circuit 240 stopspassing current, which cuts off current to the gate terminals of thefirst and second MOSFETs 262, 266. The first and second MOSFETs 262, 266turn off and the bypass current passes primarily through the bypassdiode 214 instead of the first and second MOSFETs 262, 266. When thefirst and second MOSFETs 262, 266 turn off (switch), a current spikethrough the bypass diode 214 occurs. This change in current, via thecurrent transformer 220, causes the power supply 230 to recharge and theprocess begins again. This process is a continuing loop that allows thefirst and second MOSFETs to be powered from bypass current passingthrough the bypass diode 214 while only allowing bypass current to passthrough the bypass diode 214 for a small percentage of the time.

In other words, the system 200 uses a fraction of the bypass current topower the first and second MOSFETs 262, 266 and keeps bypass currentpassing through the first and second MOSFETs 262, 266 rather thanthrough the bypass diode 214. When more power is needed, the first andsecond MOSFETs 262, 266 turn off momentarily to allow more current to beskimmed off the bypass current as the bypass current momentarily passesthrough the bypass diode 214.

A current transformer is a type of transformer used to measure highcurrents. Where high currents are too great for direct measurement viameasurement tools, a current transformer produces a reduced current thatis proportional to the current being measured. The reduced current canbe measured by current measuring instruments. Other types oftransformers can also be used, however.

In an embodiment, the first MOSFET 262 has a first source terminal, afirst drain terminal, and a first gate terminal. The second MOSFET 266has a second source terminal, a second drain terminal, and a second gateterminal. The second source terminal can be connected to the firstsource terminal. A resistor 264 can connect the first gate terminal andthe second gate terminal to the first source terminal and the secondsource terminal. In an embodiment, the resistor 264 in combination withthe latch circuit 240 can control the periodicity or duty cycle of thefirst and second MOSFETs 262, 266. In an embodiment, the system 200includes a junction box 210. The bypass diode 214, the first and secondMOSFETs 262, 266, the current transformer 220, the power supply 230, thelatch circuit 240, and the resistor 264 can reside within the junctionbox 210. FIG. 2a illustrates the circuits and devices that allow abypass current to bypass the bypass diode 214 and one (or more) group(s)of solar cells (not illustrated). It should be understood that othersets of bypass diodes, current transformers, power supplies, latchcircuits, resistors, and MOSFETs can be connected at the top and bottomof the illustration in FIG. 2 b.

In an embodiment, the first and second MOSFETs 262, 266 can remain oneven when the bypass currents 250, 252 stop flowing or approach zeroamperes. Instead current returns to flowing primarily through the groupof solar cells. In other words, the group of solar cells temporarilyceases to use the bypass diode 214 or the MOSFETs 262, 266—the group ofsolar cells returns to normal operation. The first and second MOSFETs262, 266 can be turned off after a preset period of time regardless ofthe path that current takes through the system 200 (e.g., through thegroup of solar cells or through the bypass diode 214 or the MOSFETs 262,266).

FIG. 2b illustrates embodiments of a current transformer, a powersupply, and a latch circuit. FIG. 2b is identical to FIG. 2a , exceptthat electronic devices (resistors, a capacitor, diodes, transistors, atransformer, etc.) are shown that, in this embodiment, can be parts ofthe current transformer 220, the power supply 230, and the latch circuit240.

The current transformer 220 has a greater number of windings on thesecondary winding than on the primary winding. As such, a current isgenerated in the secondary windings that is smaller than the bypasscurrent traveling through the primary windings and the bypass diode 214.Other types of transformers can also be used as well as any devicecapable or using a portion of the bypass current through the bypassdiode 214 to charge the power supply 230. In other words, the currenttransformer 220 can be any device capable of generating a power supplyinput voltage 229 when the first bypass current 250 through the bypassdiode 214 changes. When the first and second MOSFETs 262, 266 close, thefirst bypass current 250 through the bypass diode 214 spikes or rapidlyincreases. This current spike generates a current in the secondary coilsthat charges the power supply 230.

In the illustrated embodiment, the power supply 230 includes a diode232, a resistor 234, a zener diode 236, and a capacitor 238. When thefirst bypass current through the bypass diode 214 increases (e.g., via acurrent spike caused by the first and second MOSFETs 262, 266 switchingoff) the current transformer 220 generates a current and a voltage inits secondary coils. The current and voltage in the secondary coilscharge the capacitor 238. This charging continues until the voltagegenerated by the current transformer 220 equals the voltage drop acrossthe capacitor 238. A negative current and voltage would also be createdwhen the current through the bypass diode 214 decreases, except that thediode 232 prevents a reversal of current or voltage in the power supply230. In other words, while the bypass current through the bypass diode214 increases and decreases, the capacitor 238 is only charged, ratherthan discharged, because the diode 232 rectifies the current from thecurrent transformer 220.

Even before the current transformer 220 is no longer generating enoughvoltage to charge the capacitor 238, the voltage drop across thecapacitor (the latch input voltage 239) will exceed or be greater than afirst voltage threshold. When the voltage drop across the capacitor 238is greater than the first voltage threshold, the latch circuit 240 turnson and allows a control voltage from the capacitor 238 to be applied tothe gate terminals of the first and second MOSFETs 262, 266.

In an embodiment, the latch circuit 240 includes the following: a zenerdiode 242, a first resistor 244, a first bipolar junction transistor(BJT) 246, a second resistor 248, a second BJT 250, a third resistor252, a fourth resistor 254, a fifth resistor 256, and a third BJT 258.These components can be connected as illustrated in FIG. 2b . Othercomponents can be used to achieve the same functionality: passingcurrent once the latch input voltage 239 exceeds a first voltagethreshold and not passing current once the latch input voltage 239 dropsbelow a second voltage threshold. The first voltage threshold is greaterthan the second voltage threshold. In other words, the latch circuit 240has a hysteretic operation—it turns on when the latch input voltage 239rises above a first voltage threshold, but does not turn off until thelatch input voltage 239 falls below the second voltage threshold.

The first voltage threshold is determined via the combination of thethreshold voltage on the zener diode 242 and the base-emitter thresholdvoltage of the third BJT 258 (npn). Once the latch circuit input voltage239 is great enough to turn the third BJT 258 on, the second BJT 250(pnp) turns on, which in turn turns on the first BJT 246 (pnp). With thefirst BJT 246 turned on, the capacitor 238 can discharge its voltageinto the gates of the first and second MOSFETs 262, 266. The second andthird BJTs 250, 258 form a thyristor or bi-stable circuit which latcheson once the first voltage threshold is surpassed, and do not latch offuntil the latch circuit input voltage 239 falls below the second voltagethreshold. By modifying the value of the fifth resistor 256, the valueof the zener diode 242, and the value of the capacitor 238, a duty cycleof the latch circuit 240 can be modified.

The electronic devices that constitute the current transformer 220, thepower supply 230, and the latch circuit 240 are illustrative only. Otherelectronic devices could also be used and still achieve the samefunctionality: to use a small portion of the bypass current to power thefirst and second MOSFETs 262, 266 and thus enable the bypass current tobypass the bypass diode 214 (passing through the first and secondMOSFETs 262, 266 instead).

In an embodiment, the switching of the first and second MOSFETs 262, 266to an off state may not generate a large enough current spike throughthe bypass diode 214 to cause the latch input voltage 239 to exceed thefirst voltage threshold. In this situation, an embodiment as illustratedin FIG. 3 or FIG. 6 and discussed below can be implemented.

FIG. 3 illustrates an embodiment of a bypass switch circuit having apair of bi-directional bypass switches obtaining power from a voltagedrop across a pair of bypass diodes 304, 306. The system 300 includestwo bypass diodes 304, 306 connected in series. The pair of bypassdiodes, in combination, are connected in parallel to a group of solarcells (not illustrated) in a solar module 302. The group of solar cellscan be series connected to one or more other groups of solar cells inthe solar module 302. The pair of bypass diodes 304, 306 is seriesconnected to one or more other pairs of bypass diodes (not illustrated).The system 300 includes a first diode 308 series connected to a one-cellconverter 312. The first diode 308 in combination with a one-cellconverter 312 is connected in parallel to the pair of bypass diodes 304,306 and a first and second MOSFET 314, 316. In an embodiment, theone-cell converter 312 upconverts the voltage drop across the bypassdiodes 304, 306 and charges the capacitor 318 using the upconvertedvoltage. In an embodiment, the one-cell converter 312 is an electronicdevice for upconverting an input voltage and doing so while powered byone or more cells or batteries. In an embodiment, the one-cell converter312 can upconvert voltages as low as 0.7 to 0.9 volts. In other words,the one-cell converter 312 can upconvert the voltage drop across thepair of bypass diodes 304, 306 when the voltage drop is greater than orequal to 0.7 volts.

The illustrated MOSFETs 314, 316 are enhancement mode n-type MOSFETs,but p-type, depletion mode, and other transistors can also be used.Current generally passes through the group of solar cells, but when oneor more of the solar cells malfunctions, is shaded, or becomes highlyresistive for some other reason, the current instead passes through thebypass diodes 304, 306 or through the first and second MOSFETs 314, 316.When the current bypasses the group of solar cells, the current can bereferred to as a bypass current. The one-cell converter 312 takes aportion of the voltage drop across the bypass diodes 304, 306, caused bythe bypass current, and upconverts the voltage in order to charge thecapacitor 318. In other words, just as the embodiments illustrated inFIGS. 2a and 2b use bypass current in the bypass diode to turn theMOSFETs on, the embodiment in FIG. 3 uses the voltage drop across thebypass diodes 304, 306 to turn the MOSFETs 314, 316 on. Another way ofsaying this is that FIGS. 2a, 2b , and 3 use either the current orvoltage in one or more bypass diodes, to trigger the switching ofMOSFETs in order to reroute bypass current to the MOSFETs shortly afterbypass current begins passing through the one or more bypass diodes.

In an embodiment, the capacitor 318 is charged while the timer 322 is inan off state, and discharges its voltage into the gates of the MOSFETs314, 316 when the timer 322 is in an on state. In other words, in the onstate, the timer 322 connects a higher voltage portion of the capacitor318 to the gates of the MOSFETs 314, 316. In the off state, the timer322 prevents or stops a connection between the high voltage portion ofthe capacitor 318 and the gates of the MOSFETs 314, 316. In anembodiment, the capacitor 318 is configured to turn the MOSFETs 314, 316on when the timer 322 allows a control signal from the capacitor 318 toreach the MOSFETs 314, 316. In an embodiment, the timer 322 can remainon for a predetermined time. In an embodiment, the timer 322 can turnthe MOSFETs 314, 316 off when the direction of bypass current throughthe MOSFETs 314, 316 reverses. This can be done, for instance via acomparator configured to measure voltages across the MOSFETs 314, 316 todetermine when the direction of the bypass current has switched.Prematurely turning the MOSFETs 314, 316 off in this fashion causes anegligible loss of energy since each switching cycle is short (e.g., onthe order of a few seconds). In an embodiment, the timer 322 can remainoff for a predetermined time. As such, the capacitor 318 can charge to ahigh enough voltage that when the timer 322 turns on, the capacitor 318voltage will be large enough to drive the MOSFETs 314, 316 on for a timethat is larger than the time that the MOSFETs 314, 316 were off. In anembodiment, the capacitor 318 is not charged when the one or more bypassdiodes 304, 306 are not sufficiently forward biased to allow a bypasscurrent to pass through the one or more bypass diodes 304, 306.

In an embodiment, after the capacitor 318 charges for a time in whichthe timer 322 is off, the timer 322 is configured to turn on for aduration shorter than a time that it takes the capacitor voltage to dropbelow a threshold voltage of the MOSFETs 314, 316. The threshold voltageof the MOSFETs 314, 316 is a minimum voltage applied to the MOSFET 314,316 gates to turn the MOSFETs on. The timer 322 achieves a similar goalto the latch circuit illustrated in FIGS. 2a and 2b : it ensures thatthe capacitor 318 is disconnected from the MOSFET 314, 316 gates longenough to allow the capacitor 318 to recharge such that the capacitor318 has sufficient voltage to drive the MOSFETs 314, 316 on once thetimer 322 goes into the on state. The sufficient voltage can be aminimum voltage that must be applied to the MOSFET 314, 316 gates to putthe MOSFETs 314, 316 into the on state; in other words, a voltagethreshold of the MOSFETs. In an embodiment, the sufficient voltage islarge enough that the capacitor 318 voltage remains above the voltagethreshold of the MOSFETs 314, 316 for a period of time. If the capacitor318 is not allowed to sufficiently charge, then the capacitor 318voltage may quickly decrease to below the voltage threshold of theMOSFETs 314, 316 thus driving them into the off state faster thandesired. The timer 322 prevents this unstable state by ensuring that theMOSFETs 314, 316 remain off long enough to allow the capacitor 318 tosufficiently charge.

In an embodiment, the duty cycle of the timer 322 can be controlled by afixed clock. The fixed clock can be a part of the timer 322. In thisembodiment, the duty cycle of the timer 322 is unaffected by voltagesand currents outside of the timer 322 or voltages and currents reachingthe timer 322. The fixed clock is solely responsible for controlling thetimer's 322 duty cycle. In an embodiment, the timer 322 operates as athree-way switch controlled by a timing circuit and running according toa fixed clock.

In an embodiment, the duty cycle of the timer 322 can be controlled by atrigger of the timer 322. The trigger starts the timer or the timingcycle of the timer. When triggered, the timer 322 either allows voltageto pass from the capacitor 318 to the gates of the MOSFETs 314, 316 fora period of time, or stops voltage from passing from the capacitor 318to the gates of the MOSFETs 314, 316 for a period of time. In anembodiment, the trigger can have two voltage thresholds. When the firstvoltage threshold is surpassed, the timer 322 is triggered and turns on.Thus, when the first voltage threshold is surpassed, voltage from thecapacitor 318 discharges into the gates of the MOSFETs 314, 316. As thecapacitor 318 discharges voltage, a voltage across the capacitor 318decreases. Eventually, the voltage across the capacitor 318 falls belowa second voltage threshold, and the trigger turns the timer 322 off,thus preventing the capacitor 318 from discharging voltage into thegates of the MOSFETs 314, 316. While the timer 322 is off, the bypasscurrent passes through the bypass diodes 304, 306, is upconverted by theone-cell converter 312, and charges the capacitor 318.

To ensure that the voltage across the capacitor 318 is large enough todrive the MOSFETs 314, 316 on, the first and second voltage thresholdscan be greater than a voltage threshold of the MOSFETs 314, 316. Thevoltage threshold of the MOSFETs 314, 316 can be a minimum voltageapplied to the MOSFET 314, 316 gates, that that puts the MOSFETs 314,316 into an on state. In an embodiment, the first voltage threshold isgreater than the second voltage threshold. As such, the trigger has aresponse to the capacitor 318 voltage that can be described as ahysteresis. In an embodiment, the timer 322 can include a Schmidttrigger.

In the illustrated embodiment, the timer 322 has a first terminal322(a), a second terminal 322(b), and a third terminal 322(c) (althoughother configurations and numbers of terminals can also be implemented).In an embodiment, the first terminal 322(a) can be at a higher voltagethan the second terminal 322(b). For instance, the first terminal 322(a)can be connected to a higher voltage portion of the capacitor 318 (inFIG. 3, the bottom of capacitor 318), and the second terminal 322(b) canbe connected to an electrical node that is connected to a lower voltageportion of the capacitor 318 (in FIG. 3, the top of capacitor 318). Thefirst terminal 322(a) can be connected to the capacitor 318 such thatthe capacitor 318 can discharge voltage into the first terminal 322(a)of the timer 322. When turned on, the timer 322 can connect the firstterminal 322(a) to the third terminal 322(c) thus enabling the capacitor318 to discharge into the gates of the MOSFETs 314, 316. In anembodiment the capacitor 318 voltage passing through the timer 322 fromthe first terminal 322(a) to the third terminal 322(c) can be acted uponby circuitry within the timer 322 that either upconverts, downconverts,or delays the capacitor 318 voltage.

When voltage is able to pass from the first terminal 322(a) to the thirdterminal 322(b), the timer 322 is in an on state. When voltage is unableto pass from the first terminal 322(a) to the third terminal 322(b), thetimer 322 is in an off state. In an embodiment, the third terminal322(c) is connected to the second terminal 322(b) when the timer 322 isin the off state, although this configuration is not required. The offstate includes any configuration of internal circuitry in the timer 322wherein voltage does not pass from the first terminal 322(a) to thethird terminal 322(c).

In an embodiment, the timer 322 is only sometimes in control of when thecapacitor 318 can discharge. For instance, the capacitor 318 candischarge before the timer 322 is ready to turn the MOSFETs 314, 316off. In other words, the capacitor voltage 318 is too small to turn theMOSFETs 314, 316 on even when the timer 322 allows this voltage throughto the gates of the MOSFETs 314, 316. Hence, the duty cycle of theMOSFETs 314, 316 is not entirely controlled by the timer 322. In anembodiment, the timer 322 in combination with the first and secondresistors 324, 326 can control the duty cycle of the MOSFETs 314, 316.The timer 322 includes circuitry that periodically allows voltage topass from the capacitor 318 to the first and second MOSFETs 314, 316.The circuitry of the timer 322 can be controlled by a timing circuit.The timer 322 can control the duty cycle of the first and second MOSFETs314, 316. In an embodiment, the timer 322 can delay the switching on ofthe MOSFETs 314, 316 past a time when the capacitor 318 has enoughvoltage to turn the MOSFETs 314, 316 on. In other words, the timer 322does not allow the capacitor 318 to discharge voltage into the gates ofthe MOSFETs 314, 316 until a finite time after the capacitor 318 hassufficient voltage to turn the MOSFETs 314, 316 on. By implementing sucha delay in the timer 322, the capacitor 318 can be charged to a voltageabove the threshold required to turn the MOSFETs 314, 316 on. Thus, theMOSFETs 314, 316 will not turn back off as soon as the capacitor 318begins to discharge. Instead, the timer 322 delay can allow thecapacitor 318 to charge to a point where it can discharge for a periodof time before the voltage across the capacitor 318 is too low to keepthe MOSFETs 314, 316 on. In an embodiment, the timer 322 opens theconnection between the capacitor and the MOSFETs 314, 316 before thevoltage across the capacitor 318 can fall below the threshold requiredto turn the MOSFETs 314, 316 on.

When the first and second MOSFETs 314, 316 turn on (or are closed), thebypass current passes through the source and drain of the first andsecond MOSFETs 314, 316. When the first and second MOSFETs 314, 316 turnoff (are open), the bypass current passes through the pair of bypassdiodes 304, 306. By configuring the timer 322 to be open—connect thecapacitor to the gate terminals of the MOSFETs 314, 316—significantlymore often than the timer 322 is closed, the bypass current passesthrough the first and second MOSFETs 314, 316 most of the time. In thisway, the voltage drop across the bypass diodes 304, 306 can be reduced.For instance, in an embodiment, the voltage drop across the bypassdiodes 304, 306 can be maintained under 100 mV. Bypass current passesthrough the bypass diodes 304, 306 for short periods of time and onlyfor long enough to keep the capacitor 318 sufficiently charged.Sufficiently charged means having enough voltage to drive the first andsecond MOSFETs 314, 316 on (closed) when the timer 322 is open.

The system 300 can also include a first resistor 324 connected betweenthe timer 322 and the gate terminals of the first and second MOSFETs314, 316. The system 300 can also include a second resistor 326connected between the gate terminals of the first and second MOSFETs314, 316 and the source terminals of the first and second MOSFETs 314,316. In an embodiment, the above-described circuitry, aside from thesolar module 302, can be enclosed in a junction box 310.

In an embodiment, rather than using a timer 322, the system 300 canperiodically turn the first and second MOSFETs 314, 316 off whenever thevoltage across the capacitor 318 becomes too low to turn the MOSFETs314, 316 on or when voltage shows current reversal. While the MOSFETs314, 316 are off, the bypass current passes primarily through the bypassdiodes 304, 306 causing a sufficient voltage drop that the one-cellconverter can recharge the capacitor 318. When this happens, the MOSFETs314, 316 turn back on and the process continues to cycle. In anembodiment, a latch circuit, similar to that described with reference toFIGS. 2a and 2b , can replace the timer 322. The capacitor 318 providesa control voltage to the gates of the first and second MOSFETs 314, 316when the voltage across the capacitor 318 exceeds a first voltagethreshold. The capacitor 318 continues to provide the control voltage tothe gates of the first and second MOSFETs 314, 316 while the voltageacross the capacitor 318 decreases. When the voltage across thecapacitor falls below a second voltage threshold, the latch circuitturns off and the first and second MOSFETs 314, 316 turn off.

Although two bypass diodes 304, 306 are shown, a single bypass diode canalso be implemented if that bypass diode has a voltage drop that islarge enough to provide the one-cell converter 312 with sufficientvoltage to operate. The sufficient voltage is the voltage needed todrive the one-cell converter 312. In an embodiment, the sufficientvoltage can be 0.7 volts. In an embodiment, the one-cell converter 312operates when a sufficient voltage is provided from the bypass current.Thus, a sum of a first voltage across the first bypass diode 304 and asecond voltage across the second bypass diode 306 minus a third voltageacross the first diode 308 is greater than the sufficient voltage. Forexample, if the sufficient voltage is 0.7 volts and the first diode 308drops 0.7 volts, then, the first bypass diode 304 and the second bypassdiode 306 must drop at least 1.4 volts or else the one-cell converter312 will not have enough voltage to operate. In an embodiment, the firstdiode 308 has a voltage drop of less than 0.7 volts. In other words, thefirst diode 308 can be a low loss diode such as a reverse biasedSchottky diode.

In an embodiment, the first bypass diode 304 includes a positiveterminal and a negative terminal. The first bypass diode 304 is forwardbiased when current passes from the negative terminal to the positiveterminal. The second bypass diode 306 includes a positive terminal and anegative terminal. The positive terminal of the second bypass diode 306is connected to the negative terminal of the first bypass diode. Thefirst bypass diode 304 and the second bypass diode 306 are in parallelwith a group of series-connected solar cells. The first MOSFET 314 canbe any type of transistor and can therefore also be called the firsttransistor 314. The second MOSFET 316 can be any type of transistor andcan therefore also be called the second transistor 316. The drainterminal of the first transistor 314 is connected to the positiveterminal of the first bypass diode 304. The drain terminal of the secondtransistor 316 is connected to the negative terminal of the secondbypass diode 306. The source terminal of the second transistor 316 isconnected to the source terminal of the first transistor 314. Thenegative terminal of the first diode 308 is connected to the negativeterminal of the second bypass diode 306, and connected to the drainterminal of the second transistor 316. The one-cell converter 312 has afirst terminal, a second terminal, and a third terminal. The firstterminal of the one-cell converter 312 is connected to the drainterminal of the first transistor 314, and the positive terminal of thefirst bypass diode 304. The second terminal of the one-cell converter314 is connected to the positive terminal of the first diode 308. Thesecond diode 320 has a positive terminal and a negative terminal. Thenegative terminal of the second diode 320 is connected to the secondterminal of the one-cell converter 312. The capacitor 318 has a firstterminal and a second terminal. The first terminal of the capacitor 318is connected to the first terminal of the one-cell converter 312, thedrain terminal of the first transistor 314, and the positive terminal ofthe first bypass diode 304. The second terminal of the capacitor 318 isconnected to the positive terminal of the second diode 320.

The timer 322 has a first terminal 322(a), a second terminal 322(b), anda third terminal 322(c). The second terminal 322(b) of the timer 322 canbe connected to the first terminal of the one-cell converter 312, thefirst terminal of the capacitor 318, the drain terminal of the firsttransistor 314, and the positive terminal of the first bypass diode 304.The third terminal 322(c) of the timer 322 can be connected to thepositive terminal of the second diode 320 and the second terminal of thecapacitor 318. The timer 322 can control the duty cycle of the first andsecond transistors 314, 316. The first resistor 324 and the secondresistor 326 in combination with the timer 322 can control the dutycycle of the first and second transistors 314, 316. The first resistor324 can have a positive terminal connected to the gate terminal of thefirst transistor 314 and the gate terminal of the second transistor 316.The first resistor 324 can have a negative terminal connected to thefirst terminal 322(a) of the timer 322. The second resistor 326 can havea positive terminal connected to the source terminal of the firsttransistor 314, and the source terminal of the second transistor 316.The negative terminal of the second resistor 326 can be connected to thepositive terminal of the first resistor 324, the gate terminal of thefirst transistor 314, and the gate terminal of the second transistor316.

FIG. 6 illustrates an exemplary enhanced bypass switch circuit, whichcan be used to implement the enhanced diode bypass paths, such asdiscussed in FIGS. 1 and 3. For example, the circuit of FIG. 6 can beused to implement the system 300 in FIG. 3.

In one embodiment, the bypass switch circuit can be further enhanced asillustrated in FIG. 6. Typically, when the solar cells connected inparallel with the bypass transistor T1 606 in the segment between 614and 615 of the string are functioning properly to supply sufficientpower to the string, the positive end 615 of the string has a voltagehigher than the negative end 614 of the string. During such normaloperating conditions, the bypass transistor T1 606 is not activated, thetransistor's gate 604 is open, and the parasitic diode 605 is reversebiased and thus not conductive. However, if a solar panel malfunctionsor otherwise fails to produce sufficient power for whatever reason, suchas due to a foreign object blocking the light, a broken or too-weaksolar cell, or multiple weak solar cells, the voltage across the bypasstransistor T1 606 may reverse and the parasitic diode 605 of the bypasstransistor T1 606 becomes forward biased and thus conductive. In thissituation, the parasitic diode 605 of the bypass transistor T1 606reroute the electric current away from the problematic cells.

In FIG. 6, the parasitic diode 605 of the bypass transistor T1 606 isused to initially provide the pass for the bypass current, when thesolar cells connected in the segment between 614 and 615 of the stringare not producing sufficient power for the string. The parasitic diode605 is intrinsic to bypass transistor T1 606. In some embodiments, aseparate diode is used in place of the parasitic diode 605, or incombination with the parasitic diode 605.

In FIG. 6, when the parasitic diode 605 is forward biased by the stringto be conductive, the voltage drop across the parasitic diode 605 ishigher than when the bypass transistor T1 606 is activated. The voltagedrop across the parasitic diode 605 and the bypass transistor T1 606 isbetween 1 and 3 volts in one embodiment, when the parasitic diode 605 isconductive and the bypass transistor T1 606 is not activated via thetransistor's gate 604. Such a high voltage drop can lead to excessiveheat build-up in bypass transistor T1 606, as well as loss of efficiencyfor the system due to the loss of voltage in the parasitic diode 605.Also, at very high currents over long periods, the parasitic diode 605can break down. Therefore, it is desirable to reduce the voltage acrossthe parasitic diode 605. In one embodiment, the bypass transistor T1 606is a MOSFET, and the said desirable reduction in the voltage acrossparasitic diode 605 can be accomplished by activating the bypasstransistor T1 606 (e.g., via applying a voltage to the transistor's gate604) using a control circuit 620, as described below.

As illustrated in FIG. 6, the enhanced bypass switch circuit is selfpowered through the string. Diode DN1 608 is configured to pick up thenegative voltage from the parasitic diode 605 resulting from voltagereversal across the segment between 614 and 615 of the string. In oneembodiment, diode DN1 608 is a low voltage (e.g., 0.5 volts or lower)diode. The voltage drop across the parasitic diode 605 to cause theparasitic diode 605 to be conductive is sufficient to forward bias diodeDN1 608 and place diode DN1 608 in a conductive mode. When diode DN1 608is in a conductive mode, diode DN1 608 allows the capacitor C1 607 to becharged to provide an input to the single-cell converter 611.

In one embodiment, wherein diode DN1 608 is a 0.5 volt diode, thesingle-cell converter 611 is able to upconvert voltages as low as 0.3 to0.6 volts. Thus, the single-cell converter 611 can upconvert the voltagedrop across the parasitic diode 605 when the voltage drop is greaterthan or equal to 0.8 volts. The single-cell converter 611 outputs theconverted voltage through diode DN2 613, which in turn powers thecontroller 601. In one embodiment, the controller 601 is implementedusing an integrated circuit.

When powered by the capacitor C2 612, the controller 601 is configuredto selectively control the state of the bypass transistor T1 606 bysupplying a signal to the transistor's gate 604 to reduce the powerconsumed by the parasitic diode 605 of the bypass transistor T1 606.

In FIG. 6, the voltage drop across the parasitic diode 605 operates as apower source that charges capacitors C1 607 and C2 612, therebyproviding sufficient power to the controller 601 to cause the controller601 to turn the bypass transistor T1 606 on (e.g., activate the bypasstransistor T1 606) via a signal to the transistor's gate 604. Activatingthe bypass transistor T1 606 reduces the voltage drop across theparasitic diode 605 and the bypass transistor T1 606, therebyeliminating the power source to capacitors C1 607 and C2 612 and causingthem to begin discharging.

In one embodiment, when the controller 601 closes the transistor's gate604, even though the bypass transistor T1 606 may be in reverse mode,because of the linear resistive behavior of power MOSFETs in smallvoltage ranges, the bypass transistor T1 606 still becomes conductive,thus short-circuiting the parasitic diode 605.

The time it takes for capacitors C1 607 and C2 612 to discharge dictatesthe time period during which the controller 601 will keep the bypasstransistor T1 606 in an on or activated state. As such, by utilizinglarge enough C1 607 and C2 612 capacitors, a duty cycle of 100:1 or1000:1 can be achieved for the bypass transistor T1 606. Stateddifferently, by utilizing large enough C1 607 and C2 612 capacitors, theratio of the time the controller 601 can maintain the bypass transistorT1 606 in an on state, to the time the bypass transistor T1 606 remainsin an off state during which a high voltage drop across the parasiticdiode 605 charges capacitors C1 607 and C2 612, is above 100:1 (e.g., upto 1000:1 in some embodiments).

In FIG. 6, G1 controls the gate 604 of bypass transistor T1 606. WhileFIG. 6, for illustrative purposes, illustrates a single enhanced bypassswitch circuit, various embodiments may include several such circuitsconnected to different groups of solar cells, in a way similar to thearrangement in FIG. 1. Such embodiments may utilize a single controller(e.g., 601) to control the transistors utilized in each of the enhancedbypass switch circuits.

In one embodiment, by designing the charge and discharge time periods ofcapacitors C1 607 and C2 612 and/or the thresholds to activate anddeactivate the MOSFET to keep the duty cycle to less than 1/100 of thetime during which the bypass transistor T1 606 is not turned on, theoverall heat generated in the parasitic diode 605, as well as theoverall voltage loss therein, are kept to a minimum.

While FIG. 6 illustrates capacitors C1 607 and C2 612 as components thatdetermine the duty cycle of bypass transistor T1 606, similar to thecircuit of FIG. 3, a timer (e.g., implemented inside the controller 601)may also be utilized to further modify the duty cycle of bypasstransistor T1 606.

In FIG. 6, in times of normal voltage arrangement where the solar cellsconnected to the bypass transistor T1 606 in the segment between 614 and615 of the string are producing sufficient power, a voltage regulator,such as a low dropout regulator (LDO) 610 (in some cases a protectiondiode may be present at the input), is utilized to feed capacitor C2 612and hence power the controller 601. The controller 601 uses the power tocontrol the gates of other transistors via signals 603, . . . , 602.

The solution provided via the arrangement illustrated in FIG. 6 is avery cost-effective approach, with only one transistor in the segmentbetween 614 and 615 of the string, and in fact, can even reduce losses,because only one transistor is in series to the string when thetransistor is activated.

FIG. 7 illustrates an embodiment of a method for controlling electriccurrents in a photovoltaic system. In operation 700, a bypass transistor606 having a parasitic diode 605 is connected to a group of connectedsolar cells (e.g., 112). In one embodiment, the bypass transistor 606 isa MOSFET, and the group of solar cells includes one or more sets ofseries connected solar cells, with each set connected in parallel to thebypass transistor 606. When the solar cells are functioning properly toproduce sufficient power, the bypass transistor 606 is not activated,and the parasitic diode 605 is reverse biased. However, if a solar panelmalfunctions or otherwise fails to provide sufficient power for whateverreason, the voltage drop across the parasitic diode 605 causes a bypasscurrent to begin to flow across the parasitic diode 605 to reroute theelectric current away from the problematic cells. Therefore, inoperation 710, presence of a bypass current at the parasitic diode 605is monitored, and in operation 720 the detection of such a currentsignals a malfunction in one or more of the sets of solar cellsconnected to the bypass transistor 606. If a bypass current is detectedin operation 720, then in operation 730, the voltage drop across theparasitic diode 605 is used to charge a first energy storage device,such as a capacitor.

In one embodiment, the bypass switch circuit includes a diode 608configured to be powered by the voltage drop across the parasitic diode605, generated as a result of the respective solar cells failing toprovide sufficient power the string, to charge the first energy storagedevice (e.g., capacitor 607). In operation 740, a voltage converter(e.g., single-cell converter 611) is used to convert the voltage acrossthe first energy storage device. In operation 750, the voltage convertedby the voltage converter is used to charge a second energy storage unit(e.g., capacitor 612). In operation 760, the voltage across the secondenergy storage unit is used to power a controller 601. The controller601 is configured to provide control signals to bypass transistors,including the bypass transistor 606. In operation 770, the controller601 activates the bypass transistor 606 for a predetermined time period.

In one embodiment, the bypass transistor 606 is a power MOSFET; and thecontroller 601 activates the MOSFET by sending and maintaining a controlsignal to the gate 604 of the MOSFET. With the bypass transistor 606activated, the voltage across the bypass transistor 606 is reduced. Inoperation 780, the voltages across the first and second energy storagedevices begin to discharge once the voltage across the bypass transistor606 is reduced. The time period during which the bypass transistor 606is activated is determined by the discharge characteristics of the firstand second energy storage units. Once the energy storage units aredischarged to a predetermined level, the controller 601, which ispowered by the second energy storage unit, can no longer maintain thecontrol signal to keep the bypass transistor 606 activated. In operation790, then, the bypass transistor 606 is deactivated after the first andsecond storage devices discharge to a predetermined level.

In one embodiment, after the bypass current is detected, the ratio ofthe time the bypass transistor 606 is activated to the time it isdeactivated is at least 100:1. So long as a bypass current is detectedat the parasitic diode 605 in operation 720, signaling a malfunctioningsolar cell or group of cells, operations 730 to 780 are repeated todivert the current away from the problematic cells.

In one embodiment, when the group of solar cells connected to the bypasstransistor 606 is providing sufficient power to the string, the voltageregulator (e.g., LDO 610) is used to power the controller 601, whichcontrols the bypass transistors, including the bypass transistor 606.When the group of solar cells connected to the bypass transistor 606fails to provide sufficient power to the string, and thus fails to powerthe voltage regulator (e.g., LDO 610), the voltage drop across theparasitic diode 605 of the bypass transistor 606 is converted by avoltage converter (e.g., single-cell converter 611) to power thecontroller (601), as illustrated in FIG. 6.

FIG. 4 illustrates an embodiment of a method 400 for bypassing bypassdiodes in a solar energy generating system. The method 400 includes anopen latch circuit operation 402 for opening a latch circuit of acontroller when a voltage across a capacitor of the controller exceeds afirst voltage threshold. The method also includes a discharge capacitorvoltage into MOSFETs operation 404 for discharging a portion of thevoltage into a pair of bi-directional MOSFETs connected at their sourcesand controlled by the controller. The method 400 also includes a turnMOSFETs on operation 406 for turning the bi-directional MOSFETs on. Themethod 400 also includes a close latch circuit when capacitor voltagefalls below a second voltage threshold operation 408 for closing thelatch circuit when the voltage across the capacitor falls below a secondvoltage threshold. The second voltage threshold is less than the firstvoltage threshold. The method 400 also includes a turn MOSFETs offoperation 410 for turning the bi-directional MOSFETs off. This in turngenerates a current and voltage spike through the bypass diode. Themethod 400 also includes a charge capacitor using a portion of thecurrent spike operation 412 for charging the capacitor using a portionof the current spike.

The open latch circuit operation 402 opens a latch circuit of acontroller when a voltage across a capacitor of the controller exceeds afirst voltage threshold. The latch circuit is a switch that turns on orpasses current when an input voltage to the latch circuit is greaterthan or increases above a first voltage threshold and turns off when theinput voltage to the latch circuit is less than or decreases below asecond voltage threshold. The first voltage threshold can be greaterthan the second voltage threshold. As a result, the latch circuit has ahysteretic operation: as the voltage across the capacitor increases itcan surpass the first voltage threshold and turn the latch circuit on.The input voltage to the latch circuit is the same as the voltage acrossthe capacitor. With the latch circuit on, the capacitor can dischargevoltage and current through the open latch circuit. This decreases thevoltage across the capacitor. However, the latch circuit remains in anopen state even as the voltage across the capacitor (or the inputvoltage to the latch circuit) decreases below the first voltagethreshold. The voltage across the capacitor continues to decrease untilit falls below the second voltage threshold. Then the latch circuitcloses (or turns off). The capacitor voltage is a voltage across thecapacitor. The first voltage threshold is a voltage that must besurpassed in order for the latch circuit to turn on. The latch circuitturns off when the input voltage to the latch circuit falls below thesecond voltage threshold. The latch circuit can be part of a controller.The controller can be responsible for controlling when the MOSFETs openand close. In other words, the controller determines when bypass currentpasses primarily through the bypass diode and when the bypass currentpasses primarily through the bypass switches.

The discharge capacitor voltage into transistor gate 404 operation candischarge the capacitor voltage into the gate of a transistor. In anembodiment, there can be two transistors and the discharge capacitorvoltage into transistor gate 404 operation can discharge the capacitorvoltage into the gates of both transistors. In an embodiment, the one ortwo transistors can be MOSFETs. The one or two transistors can be n-typeMOSFETs. The one or two transistors can be enhancement mode MOSFETs. Inan embodiment, the one or two MOSFETs can have their sources connected.The voltage discharged into the one or more transistors can be greatenough to turn the transistors on—to allow them to pass current. Thecapacitor voltage decreases as the voltage across the capacitor isdischarged through the open latch circuit and into the one or two gatesof the one or two transistors.

The discharge capacitor voltage into MOSFETs operation 404 can dischargea portion of the voltage into a pair of bi-directional MOSFETs connectedat their sources and controlled by the controller. MOSFETs can passcurrent even in the off state. In an embodiment, the on state of theMOSFETs is one in which a majority of bypass current passes through theMOSFETs rather than the bypass diode. In an embodiment, the one state ofthe MOSFETs is one in which an inversion layer has been formed in theMOSFETs and a non-negligible current passes from the source to the drainof each MOSFET. The MOSFETs can turn on when a voltage is applied totheir gates and the voltage is above a threshold voltage for theMOSFETs. The MOSFETs turn on via the turn MOSFETs on operation 406.

The voltage across the capacitor eventually falls below a second voltagethreshold, where the second voltage threshold is lower than the firstvoltage threshold. When this happens, the close latch circuit whencapacitor voltage falls below a second voltage threshold operation 408closes the latch circuit thus preventing the capacitor from discharging.

Without the voltage from the capacitor, the MOSFETs turn off or open inthe turn MOSFETs off operation 410. In the off state, current generallydoes not pass through the MOSFETs. However, the switching causes acurrent and voltage spike through the bypass diode.

A portion of the current or voltage spike can be used to charge thecapacitor in the charge capacitor using a portion of the current spikeoperation 412. This can be done, for instance, via a transformer andassociated circuitry configured to pass current to the capacitor whenthe current through the bypass diode increases. In an embodiment, acurrent transformer is used. This charging activity takes place afterthe voltage across the capacitor has fallen below the second voltagethreshold. The charging thus raises the voltage across the capacitorabove the second voltage threshold. The charging can be sufficient toalso raise the capacitor voltage above the first voltage threshold. Thelatch circuit then opens via the open latch circuit operation 402 andthe method 400 continues repeating the operations described above.

It should be understood that while the method 400 has been describedwith reference to a single bypass diode, two or more bypass diodesconnected in series can also be used. It should further be understoodthat while the description of the method 400 appeared to have abeginning and ending operation, the method 400 is a repeating loop thatdoes not have a start or end operation.

It is clear that many modifications and variations of these embodimentsmay be made by one skilled in the art without departing from the spiritof the novel art of this disclosure. For example, the latch circuit canuse MOSFETs rather than BJTs. As another example, a single bypass MOSFETcan be used in many of the disclosed embodiments, rather than a pair ofbi-directional MOSFETs. As another example, a timer, as illustrated anddiscussed in FIG. 3, can control the duty cycle of the MOSFETs 262, 266in FIG. 2. Similarly, a periodic discharge of the capacitor 318 candetermine the duty cycle of the MOSFETs 314, 316 in FIG. 3 if the timer322 is not used or is not implemented. These modifications andvariations do not depart from the broader spirit and scope of theinvention, and the examples cited herein are to be regarded in anillustrative rather than a restrictive sense.

What is claimed is:
 1. A bypass switch circuit, comprising: a bypasstransistor having a parasitic diode, the bypass transistor to beconnected in parallel with an output of a group of solar cells; a firstdiode; a first capacitor connected in series with the first diode,wherein a path formed by the first diode and the first capacitor isconnected in parallel with the bypass transistor; a single cellconverter connected to the first capacitor to receive an input, thesingle cell converter to generate an output; a second diode connected toreceive the output of the single cell converter; a second capacitorconnected in series with the second diode; and a controller connected tothe second capacitor and configured to activate the bypass transistor inresponse to the parasitic diode being conductive.
 2. The bypass switchcircuit of claim 1, further comprising: a voltage regulator configuredto use the output of the group of solar cells to power the controllerwhen the parasitic diode is not conductive.
 3. The bypass switch circuitof claim 2, wherein the voltage regulator is a low dropout regulator. 4.The bypass switch circuit of claim 1, wherein time periods to charge anddischarge the first and second capacitors determine a duty cycle of thebypass transistor.
 5. The bypass switch circuit of claim 4, whereinafter a first time period in which the parasitic diode of the bypasstransistor is conductive, the controller activates the bypass transistorfor a second time period, and a ratio between the first time period andthe second time period is less than 1:100.
 6. The bypass switch circuitof claim 1, further comprising: a timer coupled with the controller tocontrol a length of a time period during which the controller keeps thebypass transistor activated.
 7. The bypass switch circuit of claim 1,wherein the first diode is configured to be conductive when theparasitic diode of the bypass transistor is conductive; and when theparasitic diode of the bypass transistor is reverse biased, the firstdiode is reverse biased.
 8. A method for controlling electric currentsin a photovoltaic system, the method comprising: charging a firstcapacitor, in response to a bypass current passing through a parasiticdiode of a transistor connected in parallel to an output of a group ofsolar cells, using a first diode powered by a voltage drop across theparasitic diode; converting a first voltage across the first capacitorto generate a second voltage; charging a second capacitor using thesecond voltage; powering a controller using the second capacitor; andactivating the transistor using the controller to reduce a voltage dropacross the transistor, after the first capacitor and the secondcapacitor are charged to a predetermined level.
 9. The method of claim8, wherein the first diode is not conductive when the transistor isactivated.
 10. The method of claim 9, further comprising: dischargingthe first capacitor and the second capacitor after the voltage dropacross the transistor is reduced.
 11. The method of claim 10, furthercomprising: deactivating the transistor after the first capacitor andthe second capacitor are discharged to a predetermined level.
 12. Amethod comprising: charging a first capacitor, in response to a bypasscurrent passing through a parasitic diode of a transistor connected inparallel to an output of a group of solar cells, using a first diode,wherein a first terminal of the first diode is connected to a terminalof the transistor, and a second terminal of the first diode is connectedto a terminal of the first capacitor, and wherein the first diode is notconductive when the transistor is activated; converting a first voltageacross the first capacitor to generate a second voltage; charging asecond capacitor using the second voltage; powering a controller usingthe second capacitor; and after the first capacitor and the secondcapacitor are charged to a predetermined level, activating thetransistor using the controller.
 13. The method of claim 12, furthercomprising: discharging the first capacitor and the second capacitorafter the voltage drop across the transistor is reduced.
 14. The methodof claim 13, further comprising: deactivating the transistor after thefirst capacitor and the second capacitor are discharged to apredetermined level.